ND Grads are used to balance a bright sky to the darker foreground where the cameras dynamic range would struggle to capture the data in one image.

The Medium grad filter can be used when a soft grad is just too soft to deal with brighter light on the horizon, but a hard grad is difficult to use on an uneven horizon.

The Medium Graduated filter has a wider feathered transition area of around 25mm, which means it is more forgiving of uneven horizons, and has a denser ND area. This will provide better light control to balance exposure without introducing dark lines to the image as a Hard Graduated filter would.

ND Grads can be stacked together, or with other filters, so you can respond to almost any lighting situation.